User Guide
Bromide
Ion Selective
Electrode
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IBromide Ion Selective Electrode User Guide
Table of Contents
Introduction ......................................1
Required Equipment ...............................2
Serial Dilutions ...................................3
Electrode Setup...................................4
Electrode Preparation .................................4
Checking Electrode Operation (Slope) . . . . . . . . . . . . . . . . . . . . .6
Measurement Units ...................................7
Sample Requirements .................................7
Measuring Hints......................................8
Electrode Storage.....................................9
Electrode Maintenance................................10
Analytical Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
Direct Calibration Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Small Volume Direct Calibration Technique . . . . . . . . . . . . . . . . . 18
Low Level Calibration Technique . . . . . . . . . . . . . . . . . . . . . . . .22
Known Addition Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
Electrode Characteristics . . . . . . . . . . . . . . . . . . . . . . . . .32
Electrode Response..................................32
Reproducibility ......................................32
Limits of Detection...................................32
Temperature Effects..................................33
Interferences .......................................34
Complexation .......................................35
Theory of Operation..................................36
Troubleshooting..................................38
Assistance .........................................39
Warranty...........................................39
Troubleshooting Checklist . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40
Ordering Information .............................41
Specifications ...................................42
II Bromide Ion Selective Electrode User Guide
1Bromide Ion Selective Electrode User Guide
Introduction
This user guide contains information on the preparation,
operation and maintenance for the bromide ion selective
electrode (ISE). General analytical procedures, electrode
characteristics and electrode theory are also included in this
user guide. Bromide electrodes measure free bromide ions in
aqueous solutions quickly, simply, accurately and economically.
Technical Support Chemists can be consulted for assistance
and troubleshooting advice. Within the United States call
1.800.225.1480 and outside the United States call 978.232.6000
or fax 978.232.6031. In Europe, the Middle East and Africa,
contact your local authorized dealer. For the most current
contact information, visit www.thermo.com/contactwater.
For the latest application and technical resources for Thermo
Scientific Orion products, visit www.thermo.com/waterapps.
Bromide ionplus® Sure-Flow® Solid State
Combination ISE, Cat. No. 9635BNWP
The bromide combination electrode has the sensing and
reference half-cells built into one electrode, which decreases the
amount of required solutions and reduces waste. The built-in
Sure-Flow reference junction prevents electrode clogging and
provides fast and stabile readings. The bromide combination
electrode is available with a waterproof BNC connector, Cat. No.
9635BNWP. Electrodes with a waterproof BNC connector can be
used on any ISE or mV meter with a BNC connection.
Bromide Solid State Half-Cell ISE,
Cat. No. 9435BN and 9435SC
The bromide half-cell electrode must be used with the double
junction reference electrode, Cat. No. 900200. The bromide
half-cell electrode is available with a BNC connector, Cat.
No. 9435BN, and a screw cap connector, Cat. No. 9435SC.
Electrodes with a screw cap connector require a separate cable.
2Bromide Ion Selective Electrode User Guide
Required Equipment
1. Thermo Scientific Orion ISE meter, such as the 4-Star pH/ISE
meter or 5-Star pH/ISE/DO/conductivity meter; equivalent
ISE meter; or mV meter with a 0.1 mV resolution.
Bromide electrodes can be used on any ISE or mV meter
with a BNC connection. The electrodes can also be used
on meters with a variety of inputs when an adapter cable is
used. Visit www.thermo.com/water for details.
2. Thermo Scientific Orion bromide electrode.
The 9435BN and 9435SC bromide half-cell electrodes
require a separate reference electrode, Cat. No. 900200.
3. Magnetic stirrer or Thermo Scientific Orion stirrer probe,
Cat. No. 096019. The stirrer probe can be used with 3-Star,
4-Star and 5-Star benchtop meters.
4. Volumetric flasks, graduated cylinders and beakers. Plastic
labware is required for low level bromide analysis.
5. Distilled or deionized water.
6. Bromide electrode filling solution.
Use Optimum Results™ D filling solution, Cat. No. 900063,
for the 9635BNWP bromide combination electrode.
Use inner chamber filling solution, Cat. No. 900002, and
outer chamber filling solution, Cat. No. 900003, for the
double junction reference electrode that is used with the
9435BN and 9435SC bromide half-cell electrodes.
7. 0.1 M NaBr calibration standard, Cat. No. 943506.
8. Bromide ionic strength adjuster (ISA), Cat. No. 940011.
ISA provides a constant background ionic strength for
samples and standards.
3Bromide Ion Selective Electrode User Guide
Serial Dilutions
Serial dilution is the best method for the preparation of
standards. Serial dilution means that an initial standard is diluted,
using volumetric glassware, to prepare a second standard
solution. The second standard is similarly diluted to prepare a
third standard, and so on, until the desired range of standards
has been prepared.
1. To prepare a 10-2 M NaBr standard (799 ppm bromide) –
Pipet 10 mL of the 0.1 M NaBr standard into a 100 mL
volumetric flask. Dilute to the mark with deionized water
and mix well.
2. To prepare a 10-3 M NaBr standard (79.9 ppm bromide) –
Pipet 10 mL of the 10-2 M NaBr standard into a 100 mL
volumetric flask. Dilute to the mark with deionized water
and mix well.
3. To prepare a 10-4 M NaBr standard (7.99 ppm bromide) –
Pipet 10 mL of the 10-3 M NaBr standard into a 100 mL
volumetric flask. Dilute to the mark with deionized water
and mix well.
To prepare standards with a different concentration use the
following formula:
C1 * V1 = C2 * V2
C1 = concentration of original standard
V1 = volume of original standard
C2 = concentration of standard after dilution
V2 = volume of standard after dilution
For example, to prepare 1000 mL of a 100 ppm bromide standard
from a 7990 ppm bromide standard:
C1 = 7990 ppm bromide
V1 = unknown
C2 = 100 ppm bromide
V2 = 1000 mL
7990 ppm * V1 = 100 ppm * 1000 mL
V1 = (100 ppm * 1000 mL) / 7990 ppm = 12.5 mL
4Bromide Ion Selective Electrode User Guide
Electrode Setup
Electrode Preparation
9435BN and 9435SC Bromide Half-Cell Electrode – Remove
the protective shipping cap from the sensing element and save
the cap for storage.
900200 Double Junction Reference Electrode – Prepare the
reference electrode according to the reference electrode user
guide. Fill the reference electrode with inner chamber filling
solution, Cat. No. 900002, and outer chamber filling solution,
Cat. No. 900003.
9635BNWP Bromide Combination Electrode – Remove the
protective shipping cap from the sensing element and save the
cap for storage. Fill the electrode with Optimum Results D filling
solution, Cat. No. 900063.
9635BNWP Bromide Combination Electrode
Filling Instructions
1. Lift the flip spout on the filling solution bottle to a
vertical position.
2. Insert the spout into the filling hole on the outer body of the
electrode and add a small amount of filling solution to the
reference chamber. Invert the electrode to moisten the top
O-ring and then return the electrode to the upright position.
3. Hold the electrode body with one hand and use your thumb
to push down on the electrode cap to allow a few drops of
filling solution to drain out of the electrode.
4. Release the electrode cap. If the sleeve does not return
to its original position, check if the O-ring is moist and
repeat steps 2 through 4 until the sleeve returns to the
original position.
5. Add filling solution to the electrode up to the filling hole.
Note: Add filling solution each day before using the electrode.
The filling solution level should be at least one inch above the
level of sample in the beaker to ensure a proper flow rate. The fill
hole should always be open when taking measurements.
5Bromide Ion Selective Electrode User Guide
Figure 1
9635BNWP Bromide Combination Electrode
cap
epoxy-coated
spring
cable
O-ring
fill hole
inner cone
reference
element
filling solution
chamber
inner
electrode body
outer
electrode body
6Bromide Ion Selective Electrode User Guide
Checking Electrode Operation (Slope)
These are general instructions that can be used with most
meters to check the electrode operation. Refer to the meter user
guide for more specific information.
This procedure measures electrode slope. Slope is defined
as the change in millivolts observed with every tenfold change
in concentration. Obtaining the slope value provides the best
means for checking electrode operation.
1. If the electrode has been stored dry, prepare the electrode
as described in the Electrode Preparation section.
2. Connect the electrode to a meter with a mV mode. Set the
meter to the mV mode.
3. Add 100 mL of distilled water and 2 mL of ISA into a 150 mL
beaker. Stir the solution thoroughly.
4. Rinse the electrode with distilled water and place the
electrode into the solution prepared in step 3.
5. Select either a 0.1 M or 1000 ppm bromide standard. Pipet
1 mL of the standard into the beaker and stir the solution
thoroughly. When a stable reading is displayed, record the
electrode potential in millivolts.
6. Pipet 10 mL of the same standard into the same beaker
and stir the solution thoroughly. When a stable reading is
displayed, record the electrode potential in millivolts.
7. There should be a -54 to -60 mV difference between the two
millivolt readings when the solution temperature is between
20 to 25 °C. If the millivolt potential is not within this range,
refer to the Troubleshooting section.
7Bromide Ion Selective Electrode User Guide
Measurement Units
Bromide concentration can be measured in moles per liter (M),
parts per million (ppm) or any convenient concentration unit.
Table 1
Concentration Unit Conversion Factors
Moles/Liter (M) ppm
1.0 79900
10-1 7990
1.25 x 10-2 1000
10-2 799
10-3 79.9
10-4 7.99
1.25 x 10-5 1
Sample Requirements
The epoxy body of the bromide electrode is resistant to damage
by aqueous solutions. The electrode may be used intermittently
in solutions that contain methanol, benzene or acetone. Contact
Technical Support for information on using the electrode for
specific applications.
Samples and standards should be at the same temperature. A
1 °C difference in temperature for a 10-3 M bromide solution will
give rise to about a 4% error when using the half-cell bromide
electrode, Cat. No. 9435BN and 9435SC. The combination
bromide electrode, Cat. No. 9635BNWP, when used with
Optimum Results D filling solution, produces less than a 1%
error in the same solution.
The solution temperature must be less than 80 °C.
In all analytical procedures, ISA must be added to all samples and
standards before measurements are taken.
8Bromide Ion Selective Electrode User Guide
Measuring Hints
• Stir all standards and samples at a uniform, moderate rate.
Place a piece of insulating material, such as Styrofoam or
cardboard, between the magnetic stir plate and beaker to
prevent measurement errors from the transfer of heat to
the sample.
• Always use freshly prepared standards for calibration.
• Always rinse the electrode with distilled water between
measurements and shake the electrode to remove the
water and prevent sample carryover. Do not wipe or rub the
electrode sensing element.
• Allow all standards and samples to reach the same
temperature for precise measurements.
• Concentrated samples (greater than 7990 ppm or 10-1 M
bromide) should be diluted before measurement.
• Verify the electrode calibration every two hours by placing
the electrode in a fresh aliquot of the least concentrated
standard used for calibration. If the value has changed by
more than 2%, recalibrate the electrode.
• After immersing the electrode in a solution, check the
electrode sensing surface for air bubbles and remove air
bubbles by reimmersing the electrode in the solution and
gently tapping it.
• For high ionic strength samples, prepare standards with a
background composition similar to the sample.
• The fill hole cover must be open during measurements to
ensure a uniform flow of filling solution.
• If the combination electrode is used and the electrode is
used in dirty or viscous samples or the electrode response
becomes sluggish, empty the electrode completely, hold
the junction open and flush the junction with distilled water.
Empty any water from the electrode and refill it with fresh
filling solution. Press down on the electrode cap to let a few
drops of the filling solution flow out of the electrode and
then replenish any lost solution.
9Bromide Ion Selective Electrode User Guide
Electrode Storage
Bromide Half-Cell Electrode Storage,
Cat. No. 9435BN and 9435SC
The bromide half-cell electrode should be rinsed thoroughly with
distilled water and stored dry in the air at all times. When storing
the electrode for long periods of time, cover the sensing element
with the protective shipping cap.
Double Junction Reference Electrode Storage,
Cat. No. 900200
The double junction reference electrode may be stored in
the outer chamber filling solution, Cat. No. 900003, between
sample measurements and up to one week. The filling solution
inside the electrode should not be allowed to evaporate, as
crystallization will result.
For storage longer than one week, drain the reference electrode,
flush the inside with distilled water and store the electrode dry.
Bromide Combination Electrode Storage,
Cat. No. 9635BNWP
For storage between measurements and up to one week, store
the electrode in a 4 M potassium chloride solution with bromide.
The bromide concentration of the storage solution should be
close to the least concentrated bromide calibration standard. Do
not add ISA to the storage solution. The filling solution inside the
electrode should not be allowed to evaporate, as crystallization
will result.
For storage longer than one week, drain the electrode, flush the
chamber with distilled water and store the electrode dry with the
protective shipping cap covering the sensing element.
10 Bromide Ion Selective Electrode User Guide
Electrode Maintenance
Polishing the Bromide Combination Electrode and
Bromide Half-Cell Electrode
The sensing surface of solid state electrodes can wear over time,
which causes drift, poor reproducibility and loss of response in
low level samples. The electrode can be restored by polishing
the sensing surface with a polishing strip, Cat. No. 948201. The
polishing strip can also be used if the sensing surface has been
etched or chemically poisoned.
1. Cut off about an inch of the polishing strip.
2. Hold the electrode with the sensing surface facing up.
3. Place a few drops of distilled water on the sensing surface.
4. With the frosted side of the polishing strip facing down, use
light finger pressure to place the polishing strip on top of the
sensing surface.
5. Rotate the electrode for about 30 seconds.
6. Rinse the electrode with distilled water and soak the
electrode in a 1 ppm or 10-5 M bromide standard for
ten minutes.
Bromide Combination Electrode and Double
Junction Reference Electrode Flushing
If the area between the electrode sleeve and inner cone
becomes clogged with sample or precipitate, flush the area with
filling solution or distilled water.
1. Hold the electrode body with one hand and use your thumb
to push down on the electrode cap to drain the electrode.
Push down on the cap until all the filling solution is drained
from the chamber.
2. Fill the electrode with distilled water and then push down on
the cap until all the water is drained from the chamber.
3. Fill the electrode with fresh filling solution up to the fill hole.
Push down on the cap to allow a few drops of filling
solution to drain out of the electrode and replenish the lost
filling solution.
11Bromide Ion Selective Electrode User Guide
Disassembling and Reassembling the Bromide
Combination Electrode
Note: Disassembly is usually not required and should not be
done unless a thorough cleaning is required.
1. Tip the electrode so the filling solution moistens the O-ring
on the electrode body. Hold the electrode body with one
hand and use your thumb to push down on the electrode
cap to drain the electrode.
2. Unscrew the cap counterclockwise and then slide the cap
and spring up the cable.
3. Hold the outer sleeve with one hand and firmly push down
on the threaded portion with your thumb and forefinger to
separate the inner body from the sleeve.
4. Grasp the inner cone with a clean, lint-free tissue and
withdraw the body from the sleeve using a gentle twisting
motion. Do not touch the pellet above the cone, as it will
damage to the pellet. Rinse the outside of the electrode
body and the entire sleeve with distilled water. Allow it to
air dry.
5. Moisten the O-ring on the electrode body with a drop of
filling solution. Insert the screw-thread end of the electrode
body into the tapered, ground end of the sleeve.
6. Push the body into the sleeve using a gentle twisting motion
until the bottom surface of the inner cone is flush with the
tapered end of the sleeve.
7. Place the spring onto the electrode body and screw on the
cap. Refill the electrode with filling solution.
12 Bromide Ion Selective Electrode User Guide
Analytical Techniques
A variety of analytical techniques are available to the analyst. The
following is a description of these techniques.
Direct Calibration is a simple procedure for measuring a large
number of samples. Only one meter reading is required for each
sample. Calibration is performed using a series of standards.
The concentration of the samples is determined by comparison
to the standards. ISA is added to all solutions to ensure that
samples and standards have similar ionic strength.
Low Level Calibration is a similar to the direct calibration
technique. This method is recommended when the expected
sample concentration is less than 0.4 ppm or 5 x 10-6 M
bromide. A minimum three point calibration is recommended
to compensate for the electrode’s non-linear response at these
concentrations. A special calibration standard preparation
procedure is the best means of preparing low level calibration
standards.
Incremental Techniques provide a useful method for measuring
samples, since a calibration is not required. The different
incremental techniques are described below. They can be
used to measure the total concentration of a specific ion in the
presence of a large (50 to 100 times) excess of complexing
agents. As in direct calibration, any convenient concentration
unit can be used.
Known Addition is useful for measuring dilute samples,
checking the results of direct calibration (when no
complexing agents are present), or measuring the total
concentration of an ion in the presence of an excess
complexing agent. The electrode is immersed in the sample
solution and an aliquot of a standard solution containing the
measured species is added to the sample. From the change
in potential before and after the addition, the original sample
concentration is determined.
13Bromide Ion Selective Electrode User Guide
Table 2
Recommended Measuring Techniques
Direct
Calibration
Small
Volume
Direct
Calibration
Low Level
Calibration
Known
Addition
[Br-] < 0.4 ppm ✔
[Br-] > 0.4 ppm ✔ ✔
[Br-] > 1.0 ppm ✔
Occasional
Sampling ✔
Small sample
volume ✔
Large number
of samples ✔ ✔ ✔
Reduce
chemical
usage
✔
Field
measurement ✔
Ionic strength
greater than
0.1 M
✔
Complicated
background ✔
14 Bromide Ion Selective Electrode User Guide
Direct Calibration Technique
Typical Direct Calibration Curve
In the direct calibration procedure, a calibration curve is
constructed either in the meter memory or on semi-logarithmic
paper. Electrode potentials of standard solutions are measured
and plotted on the linear axis against their concentrations on the
log axis. In the linear regions of the curves, only two standards
are needed to determine a calibration curve. In non-linear
regions, more points must be taken. These direct calibration
procedures are given for concentrations in the region of linear
electrode response. Low level measurement procedures are
given in a following section for measurements in the non-linear
electrode region.
Figure 2
Typical Direct Calibration Curve
+60
+80
+100
+120
+140
+160
+180
10-6
.1 1 10 102103
Molarity
ppm Br-
10-5 10-4 10-3 10-2
+40
-40.0
-20.0
0
+20
Electrode
potential
(mV)
-57 mV
10-fold change
15Bromide Ion Selective Electrode User Guide
Direct Calibration Overview
The following direct measurement procedures are recommended
for moderate to high level measurements. Samples must be in
the linear range of the electrode – greater than 0.4 ppm or
5 x 10-6 M bromide. A two point calibration is sufficient,
although more points can be used. When using an ISE meter,
sample concentrations can be read directly from the meter.
When using a mV meter, a calibration curve can be prepared
on semi-logarithmic graph paper, or a linear regression (against
logarithmic concentration values) can be performed using a
spreadsheet or graphing program.
Calibration Hints
• Standard concentrations should bracket the expected
sample concentrations.
• Always add 2 mL of ISA, Cat. No. 940011, per 100 mL of
standard or sample.
• For high ionic strength samples that have an ionic strength
of 0.1 M or greater, prepare standards with a background
composition similar to that of the samples, or measure the
samples using the known addition method.
• During calibration, measure the least concentrated standard
first, and work up to the most concentrated standard.
Direct Calibration Setup
1. Prepare the electrode as described in the Electrode
Preparation section. If using the 9635BNWP combination
bromide electrode, fill the electrode with Cat. No. 900063.
If using the 9435BN or 9435SC half-cell bromide electrode
with the 900200 reference electrode, fill the reference
electrode with inner chamber filling solution, Cat. No.
900002, and outer chamber filling solution, Cat. No. 900003.
2. Connect the electrode to the meter.
3. Prepare at least two standards that bracket the expected
sample range and differ in concentration by a factor of ten.
Standards can be prepared in any concentration unit to suit
the particular analysis requirement. See the Serial Dilution
section for instructions on how to prepare standards. All
standards should be at the same temperature as the
samples. For details on temperature effects on electrode
performance, refer to the Temperature Effects section.
16 Bromide Ion Selective Electrode User Guide
Direct Calibration Procedure Using a
Meter with an ISE Mode
Note: See the meter user guide for more specific information.
1. Add 100 mL of the less concentrated standard and 2 mL of
ISA to a 150 mL beaker and stir the solution thoroughly.
2. Rinse the electrode with distilled water, blot it dry and place
it into the beaker with the less concentrated standard. Wait
for a stable reading and adjust the meter to display the value
of the standard, as described in the meter user guide.
3. Add 100 mL of the more concentrated standard and 2 mL
of ISA to a second 150 mL beaker and stir the solution
thoroughly.
4. Rinse the electrode with distilled water, blot it dry and place
it into the beaker with the more concentrated standard.
Wait for a stable reading and adjust the meter to display the
value of the second standard, as described in the meter user
guide.
5. Record the resulting slope value. The slope should be
between -54 and -60 mV when the standards are between
20 and 25 °C.
6. Add 100 mL of sample and 2 mL of ISA to a clean 150 mL
beaker and stir the solution thoroughly.
7. Rinse the electrode with distilled water, blot it dry and place
it into the sample. The concentration of the sample will be
displayed on the meter.
Note: Other solution volumes may be used, as long as the ratio
of solution to ISA remains 50:1.
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